Concrete Block Lab 3e: First Test Blocks from The Cinva Ram

These blocks were made with the trial run of the Cinva Ram on April 6, 2000. (For photos of the making, click here.) The block images were taken on 19 April. The cracks appear to be a result of the machine. Though we didn't know it at the time, the axle that pushes up the bottom plate on the cinva ram was bent (I overloaded the machine the first time I tested it and apparently bent the axle. I think the bottom of the machine wasn't pushing up uniformly; the bent axle caused a slight amount of rotation. That's my best guess, anyway).

We started choosing mixes based on the results of the last lab. Then we started winging it, based on observations we made about the perfromance of the raw blocks. For instance, red sand was quickly recognized as making a more solid raw block, so we did a series of tests with red sand as a primary constituent, and varying the amount of cement. (Mixes 6, 7, 9 & 11).

Some Conclusions from this lab's work:

  1. The amount of water should be arrived at based on the "feel" of the mix; it's not a strictly quantitive thing. If you take a handful and squeeeze it together, and it holds well, without being too wet, it's probably about right. The natural water content of the materials is something you might not be able to control, so it's important to be able to judge by feel.
  2. Delivering the blocks can be tricky. We slid the blocks off the bottom plate of the Cinva onto a plastering hawk, then onto the counter to dry. If you were going into production, this would be too fussy. But the blocks were not solid enough to pick up with one's hands, like they show elsewhere. I'm not sure what this is about.
  3. The Red Sand helps a lot to make the raw block more stable. I'm guessing it's the natural clay content. (For those who don't know it, Red Sand in Mississippi is the sandy red soil you see in the landscape. It's used for a lot of fill purposes where you need good compaction. It's placed under roadbeds, for instance. It has some clay in it, but I don't know how much. We need to get some assistance from Civil Engineering, probably, to understand the constituents of the soil.)

Compressive Strength Test: We broke the blocks in 2 pieces and crushed one in the Soiltest machine in our lab. The psi was determined by dividing the total load carried by the approximate face area.

Water Blast Test: We used a household pressure washer (1200 psi rating) with a rotating tip and trained it on the block at 4" from the face, normal to the surface. Blocks were generally blasted for 2 minutes, unless it was clear that it wouldn't last the full length of time. (The mixes with no cement content didn't last).

For photos of the water testing, click here.

Block # Image (Click on the thumbnail for a larger image) Portland Cement Red Sand Conc Sand Fine Sand Vermiculite Wash Gravel Water Comp. Strength Water Blast (Click on the thumbnail for a larger image) Remarks
1   3   5     2 0.75 1407 psi
2 minutes
2   3   5     2 1 2666 psi
2 minutes
Very solid block after it dried 
3   2 4 4       0.25 2753 psi
2 minutes
4     5 3   2   0.5 74 psi
4 seconds
5   1 1 1 1 1 1 0.75 750 psi
2 minutes
"One of Everything" mix
6     6         0.25 151 psi
3 seconds
Red Sand only. 
7   2 8         0.75 483 psi
2 minutes
8   1 4 1 2 1   0.75 1145 psi
2 minutes
9   1 9         0 333 psi
2 minutes
Red Sand was very wet when it came out of the bag, so we didn't add any water.
10   2 5 1 1 1   1 1761 psi
2 minutes
11   3 7         0.25 1076 psi
2 minutes
Very fine grain, but crumbly now. 
12               1843 psi
2 minutes
Left Over Mix: This is a mixture of left over portions of all of the above.
13                 2349 psi

51 seconds

This is a preliminary test block of unknown mix.

Last Updated on 4/20/00
By Nils Gore